<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>

<body>
    <div id="app">
        <ul>
            <li v-for='item in list'>{{item}}</li>
        </ul>
        <button @click="add">增加</button>
        <button @click="modify">修改</button>
    </div>
    <script type="text/javascript" src="js/vue.js"></script>
    <script type="text/javascript">
        var vm = new Vue({
            el: '#app',
            data: {
                list: ['apple', 'orange', 'banana']
            },
            methods: {
                add: function() {
                    this.list.push('mango')
                },
                modify: function() {
                    this.$set(this.list, 1, 'pear')
                }
            }
        });
        // 点击增加的按钮, 观察界面
        // 点击修改的按钮, 观察界面, 如何解决这个问题?
    </script>
</body>

</html>